This “land cruiser” was a self-propelled platform for the 800mm Schwerer Gustav artillery piece also made by Krupp—the heaviest artillery weapon ever constructed by shell weight and total gun weight, and the largest rifled cannon by calibre. This gun fired a 7-tonne projectile up to 37 km (23 miles) and was designed for use against heavily fortified targets. The Landkreuzer P. 1500 Monster was to be 42 m (138 ft) long, weighing 1500 tonnes, with a 250 mm hull front armor, four MAN U-boat (submarine) marine diesel engines, and an operating crew of over 100 men. The main armament was to be an 800 mm Dora/Schwerer Gustav K (E) gun, and with a secondary armament of two 150 mm sFH 18/1 L/30 howitzers and multiple 15 mm MG 151/15 autocannons. The main armament could have been mounted without a rotating turret, making the vehicle a self-propelled gun rather than a tank. Such a configuration would have allowed the P. 1500 to operate in a similar manner to the original 800mm railroad gun and Karl 600mm self-propelled mortars, launching shells without engaging the enemy with direct fire.
Development of the Panzer VIII Maus had highlighted significant problems associated with very large vehicles, such as their destruction of roads/rails, their inability to use bridges and the difficulty of strategic transportation by road or rail. The bigger the vehicle, the bigger these problems became. Propulsion had also proved problematic in the development of the Maus: The prototype had failed to meet its specified speed requirements which meant that even larger vehicles such as the P. 1500 were likely to be slow-moving.